Then came even better news. A study by the National Institute of Diabetes and Digestive and Kidney Diseases punched a kolache-sized hole in the idea that cutting carbs works better than cutting fat for weight loss. Researchers brought 19 obese volunteers into a lab and kept them there for two weeks. They fed half of them a low-carb diet and another half a low-fat one. Both groups cut their calories by 30 percent. The results, published in Cell Metabolism, showed that the two diets worked equally well: Everyone lost about a pound of body fat.
In other words, you and that croissant might as well start scouting one-bedroom apartments. You’ll probably get married, and the rent’s too high in this city anyway.
“The great thing about this study is that it is strong science,” Susan Roberts, a professor of nutrition at Tufts University, told me in an email. “So much of what gets published in nutrition ... these days is weak stuff: non–compliant participants, poor methods, not enough subjects, self-reported data, etc.”
This study, by contrast, was perfectly controlled. And though it relied on obese participants, it likely would have yielded similar results for people who were simply overweight.
The latest research does away “with the pervasive nonsense that there is something magical about high-fat diets that melt away body fat through promoting fat oxidation,” Roberts said. That idea was popularized by the ketogenic diet, which was originally intended for epileptic children but has since been adapted by healthy adults who try to shed pounds by eating almost no carbs whatsoever.
But Roberts and other experts suggested it’s not quite time to put a ring on that Twinkie. The paper didn’t address whether it’s easier to keep a low-carb or low-fat diet in the real world. Some studies have found that people lose more weight on low-carb diets, but that might be because they end up cutting more calories overall.
It’s worth applying these findings cautiously. Certain carbs, like the types of added sugars found in soda, do little good and lots of harm. Meanwhile another type of carb, fiber, has shown to be beneficial for weight loss in some studies.
Instead, what this latest research suggests is that Americans should end our fixation with—or love of—one macronutrient or another. The ‘80s were all about reducing fat. In the ‘90s, carbs became the new culprit. But it takes a combination of protein, plants, and fat to either lose weight or maintain a healthy one.
“We can’t distill our messages about what to eat to down to a single nutrient,” Roberts says. “That is just too simplistic to be effective.”
Yoni Freedhoff, an obesity expert at the University of Ottawa, said most nutrition research misses the most important aspect of diets: sustainability. “It doesn’t matter one iota whether or not there’s a marginal difference between calorie cuts from carbs or fats or proteins or whatever on short-term weight loss and body-fat percentages," he said. “Obesity is a chronic condition. Consequently, treatment by definition needs to be lifelong.”
As in love, it seems, the only thing that matters in weight loss is which diet you can commit to for the long haul.
* This article has been updated to clarify that the findings in the hominin study are theoretical.